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Interferometer at Llano de Chajnantor Observatory in Chile
The
Cosmic Background Imager
(or
CBI
) was a 13-element
interferometer
perched at an elevation of 5,080 metres (16,700 feet) at
Llano de Chajnantor Observatory
in the
Chilean
Andes
. It started operations in 1999 to study the
cosmic microwave background radiation
and ran until 2008.
CBI conducted measurements at frequencies between 26 and 36
GHz
in ten bands of 1 GHz
bandwidth
. It had a resolution of better than 1/10 of a degree. (In comparison, the pioneering
COBE
satellite, which produced the first detection of fluctuations in the microwave background in 1992, had a resolution of about 7 degrees.) Among the key findings of the CBI is the fact that fluctuations which have a small size on the sky are weaker than fluctuations which have a large size on the sky, which confirmed earlier theoretical predictions. More technically, CBI was the first experiment to detect intrinsic anisotropy in the
microwave
background on mass scales of galaxy clusters; it provided the first detection of the
Silk damping
tail; it found a hint of excess power at high-l multipoles (CBI-excess) than expected from the
ΛCDM
model; and it detected fluctuations in the
polarization
of the microwave background obtaining the first detailed E-mode polarization spectrum providing evidence that it is out of phase with the total intensity mode spectrum.
The CBI was built at the
California Institute of Technology
, and employed sensitive radio amplifiers from the
National Radio Astronomy Observatory
; two similar experiments are the
Very Small Array
, operated on the island of
Tenerife
, and the
Degree Angular Scale Interferometer
, operated in
Antarctica
. Both of these experiments used radio interferometry to measure CMB fluctuations at lower resolution over larger areas of the sky. Another experiment operated from Antarctica, the
Arcminute Cosmology Bolometer Array Receiver
, used total power (bolometric) detection and a single antenna at higher frequency and similar
angular resolution
to obtain results comparable to the CBI. The confluence of these and other CMB experiments employing different measurement techniques in recent years is a great triumph of observational cosmology.
CBI was a collaboration among a number of institutions in the US and Europe. It still closely collaborates with Chilean institutions
Universidad de Chile
and
Universidad de Concepcion
through the Chajnantor Observatory.
In 2006, new 1.4 m antennas replaced the old 0.9 m dishes for more high-resolution studies in total intensity mode. During this stage, CBI was called
CBI-2
.
In June 2008, CBI-2 stopped the observations and the 13-antenna instrument was removed from its mount. The new
QUIET telescope
instrument was installed in August 2008 on the CBI mount, replacing CBI-2 .
See also
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External links
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